I run the 62st, which is the slightly older version of the 64. They are similar in every way physically. The 64 has the ability to pick-up GLONASS which adds some accuracy, but not a deal breaker. The 62 can hold about 2,000 waypoints while the 64 can hold around 5,000. I've never run out of room to add waypoints with the 62.
Prices seem to be running about the same for the 62S and 64S, so I would just find the cheapest one and run with it. While I have the ST, I agree with other posters that the ST is useless since I run the ONXmaps anyway. The pre-loaded maps that come with the ST are obsolete once you have the ONX. I would also agree that battery life is less than I'd like, but it's not horrible.
Just to note, I have a Garmin Montana and Oregon for work. I much prefer the 62/64 over the touch screen versions. With the touch screens, it seems like they want to drop a pin anytime you have your finger on the screen for more than a second or two. Very annoying. The Montana is also huge. Way too big for my likes.